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Cosworth Low expansion Piston to wall clearance EJ255

Practical Engine Building

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Hi there!

I'm Building my first engine, an EJ255. I have opted for the Cosworth PA2667 Piston.

The alloy is a proprietary alloy but acknowledged and marketed as a 4032 type low expansion alloy.

For the EJ255 the Cosworth spec sheet recommends a .0025'-.004' PTW clearance. Being a daily driver and considering my choice of a Borg Warner efr7163r turbo (60lbs/min) I' have decided to coat the crowns with a ceramic heat coating and keep it at .0025'-.0027' clearance.

I have read in some of Andre's answers on the topic that the manufacturers generally play it safe with clearances. Which was/is my thought as well.

However my machinist is Leigh Bird of Deshele Performance and I do take his advice and experience with the EJ platform very seriously. He has recommended a .003' clearance. However I feel that he thinks more in terms of high performance race engines where I agree, However I would like to keep it as tight as I safely can. I will discuss this with him as well.


I'd love to hear other experiences and thoughts on this forum.

Thanks you!


Hello Thomas my experience is exactly as your engine machinist 0.003 would be where i would setting it also even with the coatings. The ej engine is not noted for there great cooling ability around all the bores evenly

Regards Ross

Thanks for sharing your experience Ross,

I have the Dominic Arcia cylinder 4 coolant hose installed to help even out cylinder #4 with its coolant flow issues.

I did fail to mention my peak power estimate of 400whp on 98ron 450-500whp on e85? This is not a goal, more a peak power estimate as response is my ultimate goal.

We have settled for. 0028 I will mention your opinion and make a final decision tommorow.



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